JPH05147957A - Production of quartz glass molded body for ultraviolet laser - Google Patents

Abstract

PURPOSE:To provide a synthetic quartz glass molded body having high transmittance to light having <=200nm wavelength without deteriorating homogeneity for excimer laser. CONSTITUTION:A synthetic quartz glass molded body free from striae in at least the direction of transmission of light is kept at a temp. within the range of 800-1500 deg.C and at least 100 DCV/cm DC voltage is impressed between opposite two faces of the molded body to produce a quartz glass molded body for excimer laser.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical quartz glass molding having excellent stability against irradiation of ultraviolet rays, especially excimer laser, and more particularly to an optical system of a stepper using an excimer laser as a light source, especially ArF. The present invention relates to a method for producing a quartz glass molded body for excimer laser, which is suitable for a quartz glass molded body forming a stepper optical system of an excimer laser and has excellent transmittance.

[0002]

2. Description of the Related Art In recent years, with the high integration of LSIs, a submicron unit drawing technique is required for an optical lithography technique for drawing an integrated circuit pattern on a wafer. In order to perform finer line width drawing, the wavelength of the light source of the exposure system has been shortened. Particularly recently, KrF excimer laser light (wavelength 248 nm) and Ar are used as light sources for exposure.
F excimer laser light (wavelength 193 nm) is considered,
Even in glass materials used as optical members, 25
The transparency of light having a wavelength of 0 nm or less is drawing attention as an extremely important characteristic.

Generally, a material exhibiting sufficient transmissivity in this wavelength range is not only glass as quartz glass but also quartz glass is produced by flame hydrolysis of silicon tetrachloride or the like. Unless it is a synthetic quartz glass, it does not give a substantially sufficient transmittance. On the other hand, glass materials that make up optical components such as lenses used in optical systems in excimer laser steppers require extremely strict homogeneity in order to obtain a uniform image. In order to apply to the above, a process requiring a very long time such as a homogenizing process and an annealing process is required. Further, in general, a molding step for molding a synthetic quartz glass material into a desired shape is industrially necessary.

Since the processing step and molding step performed to impart homogeneity to this synthetic quartz glass are carried out at a high temperature for a long time, the homogenized synthetic quartz glass molded article is processed and shaped. Atmosphere in process, jig,
Contamination from the furnace material and the like results in deterioration of the ultraviolet light transmittance of the synthetic quartz glass. Contamination of the synthetic quartz glass due to such a step significantly reduces the transmittance of the synthetic quartz glass, particularly in the vacuum ultraviolet region (wavelength of 200 nm or less), and even in the excimer laser light, the wavelength of Ar having a particularly short wavelength is reduced.
This is a serious problem in the optical system of a stepper using an F excimer laser as a light source.

Although efforts have been made to reduce the pollution of the synthetic quartz glass molded body in such a process,
The furnace materials and jigs used for heat treatment at high temperature are made of materials such as alumina, zirconia and graphite that contaminate synthetic quartz glass, and the transmittance of light with a wavelength of 200 nm or less is synthetic quartz glass molding. The transmittance in this region of the homogenized quartz glass does not meet the criteria desired in stepper optics, since even slight contamination of the body leads to a significant reduction.

[0006]

DISCLOSURE OF THE INVENTION The present invention is a synthetic quartz glass molding having homogeneity for excimer laser, which has been subjected to homogenization treatment and molding treatment for imparting homogeneity necessary for an excimer laser optical system. With respect to the above, it is an object of the present invention to provide a method for recovering the transmittance of light having a wavelength of 200 nm or less without impairing the homogeneity. That is,
The present invention provides a synthetic quartz glass molded body having no striae at least in the light transmission direction at a temperature in the range of 800 ° C. to 1500 ° C. while at least 100 DCV / A method for producing a quartz glass molded body for an excimer laser, which is characterized by applying a DC voltage of cm.

In the present invention, as a material, the optical characteristics necessary for constructing an excimer stepper optical system, that is,
A shape that is suitable for forming optical members such as lenses and prisms that has no striae in the direction of light transmission, has a highly uniform refractive index distribution, and has no residual distortion, that is, a cylindrical shape. A synthetic quartz glass molded body having a prismatic shape or a shape similar to these is used. These synthetic quartz glass molded bodies have undergone at least one heat treatment step among the homogenization step, the molding step, and the annealing step in forming the above-mentioned characteristics and shape. In the region of up to 180 nm, it has more or less absorption of light due to contamination during the heat treatment process.

In order to maximize the effect of the present invention, the purity of the raw material is improved, and the pollution in each step is reduced as much as possible, so that the synthetic quartz glass molding of the starting material is
Although it is desirable to minimize the light absorption in the wavelength region of 00 nm or less, the present invention does not depend on the degree of light absorption of the starting material in the wavelength region of 200 nm or less.

The inventors of the present invention have found that absorption of light having a wavelength of 200 nm or less caused by such contamination by heat treatment disappears by applying a high DC voltage at a predetermined temperature to the synthetic quartz glass molded body. I have found Moreover, in this case, it has been found that the optical characteristics other than the light transmittance required for forming the stepper optical system are not deteriorated except for the residual distortion. Since the residual strain is a thermal strain, when the treatment temperature of the present invention is set to, for example, 1000 ° C. or higher, the cooling rate is increased to increase,
In the present invention, the residual strain can be sufficiently reduced by appropriately setting the cooling rate after the voltage application process, which is a problem in practical use.

In the present invention, the application of the DC voltage is 80
It is desirable to operate at a temperature within the temperature range of 0 ° C to 1500 ° C. When the DC voltage is applied at a temperature of 800 ° C. or lower, no improvement in light transmittance is confirmed, and when applied at a temperature of 1500 ° C. or higher, the insulator suitable for high voltage becomes extremely thick, and the structure It is not good. Further, the DC voltage applied preferably has a voltage gradient of 100 DCV or more per 1 cm of the synthetic quartz glass molded body.

If the DC voltage applied to the synthetic quartz glass molded body is 100 DCV / cm or less, it is difficult to achieve a sufficient improvement in light transmittance. On the other hand, the higher the voltage is, the more effective it is. However, at a DC voltage of 3000 DCV / cm or more, the appropriate insulating material becomes extremely thick,
Structurally unfavorable. In the present invention, the residual strain is determined during the cooling of the heat treatment, and this is reduced to a level where there is no practical problem (5 nm / cm or less) by gradually cooling at a cooling rate of 5 ° C./hour or less. be able to. At this time, the characteristics are not affected whether or not the voltage is applied.

In the present invention, high-purity graphite is used as the electrode. Since graphite itself is a source of contamination for the synthetic quartz glass molded body, a high-purity graphite should be selected as much as possible before use. Depending on the temperature, it is preferable to perform baking at a temperature 50 to 100 ° C. higher for at least 100 hours. Impurities in graphite are removed by the air-baking treatment of the electrode, and the present invention can be effectively carried out.

The residual strain of the material can be set during the cooling of the present treatment step as described above, and therefore the restriction of the starting material may be removed. In this case, the homogeneity of the refractive index distribution also remains. If the distortion is not limited, there is no confirmation method, so it cannot be practically limited.

[0014]

According to the present invention, a synthetic quartz glass molded body having no striae at least in the light transmitting direction is provided at 800 ° C to 1500 ° C.
Since a DC voltage of at least 100 DCV / cm is applied to the two opposing surfaces of the glass molded body while maintaining the temperature within the range, contamination of the synthetic quartz glass molded body due to heat treatment or the like is electrically removed. It will be 200n
Absorption of light having a wavelength of m or less does not occur.

[0015]

EXAMPLES The embodiments of the present invention will be described below with reference to examples, but the present invention is not limited to these examples and explanations. Example 1. The synthetic quartz glass compact used in this example is obtained by subjecting synthetic quartz glass to homogenization treatment, shaping it into a cylindrical shape having a diameter of 100 mm and a thickness of 30 mm, and then annealing it at 1150 ° C. This synthetic quartz glass molded body has no striae in three directions and has a uniform refractive index distribution, and the difference (Δn) between the maximum and minimum values of the refractive index at a thickness of 1 cm is Δn = It was 2 × 10 ⁻⁶ .

After polishing the synthetic quartz glass molded body, the transmittance of light in the wavelength region of 240 nm or less was measured by a vacuum ultraviolet spectrophotometer after polishing, and high purity graphite electrodes were formed on both end faces of the synthetic quartz glass molded body. Was set and placed in a vertical tubular furnace having a quartz glass tube as a furnace core tube. Applying a DC voltage to the synthetic quartz glass molded body was carried out with nitrogen at 50
While heating while flowing at 0 ml / min, when the temperature reached 1150 ° C, a DC voltage of 3000 V was applied to both ends,
It was left for 5 hours while applying a DC voltage. When 5 hours had passed, the energization was stopped and the mixture was slowly cooled to room temperature at a cooling rate of 5 ° C / hour. Remove the synthetic quartz glass molded body to which a DC voltage was applied from the vertical tubular furnace, re-polish it,
The light transmittance was measured in the same manner.

A synthetic quartz glass molded body after application of a DC voltage,
That is, FIG. 1 shows a chart of the light transmittance of Example (I) of the present invention and the synthetic quartz glass molded body (II) before applying a DC voltage. As shown in FIG. 1, 190 observed in the synthetic quartz glass molded body (II) before applying the DC voltage.
Absorption having a peak at nm is not observed at all in the synthetic quartz glass molded product (I) after the application of the DC voltage, and particularly the transmittance at 193 nm which is the oscillation wavelength of the ArF excimer laser is significantly improved. On the other hand, when the strain of the synthetic quartz glass compact subjected to the voltage application treatment was measured with a strain gauge, it showed a suitable value of 2 nm / cm or less. The interference fringes showing the refractive index distribution of the quartz glass body are shown in FIG. It can be seen that even after the treatment, it has excellent homogeneity required for the optical member.

Comparative Example 1 A synthetic quartz glass molded body which was subjected to homogenization treatment under the same conditions as the synthetic quartz glass molded body used in the example, and was molded,
Place it in a vertical tube furnace and keep 300 at both ends at 750 ° C.
After applying a DC voltage of 0 V for 5 hours, it was cooled to room temperature at a cooling rate of 5 ° C./hour. FIG. 3 shows the results of measuring the transmittance of the treated quartz glass body with a vacuum ultraviolet spectrophotometer. Absorption with a peak at 190 nm has not disappeared.

Comparative Example 2 A synthetic quartz glass molded body obtained by subjecting to a homogenization treatment under the same conditions as the synthetic quartz glass molded body used in the example, and molding
Place it in a vertical tube furnace and put it at 1150 ° C for 25
After applying a DC voltage of 0 V for 5 hours, it was cooled to room temperature at a cooling rate of 5 ° C./hour. After cooling, the synthetic quartz glass molded body to which a DC voltage was applied was measured for light transmittance with a vacuum ultraviolet spectrophotometer. The results are shown in FIG. Absorption with a peak at 190 nm has not disappeared.

[0020]

According to the present invention, a synthetic quartz glass molded body having no striae at least in the light transmitting direction is formed at 800 ° C. to 150 ° C.
While maintaining the temperature within the range of 0 ° C., a DC voltage of at least 100 DCV / cm is applied to the two opposite surfaces of the glass molded body, so that contamination during the heat treatment is electrically removed. The synthetic quartz glass molded body of the present invention has a uniform refractive index distribution and is excellent in light transmittance as compared with the conventional synthetic quartz glass molded body. Therefore, the optical member of the present invention can obtain a clearer image than the conventional optical member.

[Brief description of drawings]

FIG. 1 shows a light transmittance curve (I) of a synthetic quartz glass molded body to which a DC voltage is applied and a light transmittance curve (II) of a synthetic quartz glass molded body to which a DC voltage is not applied according to one embodiment of the present invention. It is a light transmittance curve figure.

FIG. 2 shows a refractive index distribution of a synthetic quartz glass molded body after applying a DC voltage according to another embodiment of the present invention, showing a difference (Δn) between the maximum value and the minimum value of the refractive index per 1 cm of thickness. , Δn =
It is explanatory drawing which shows the interference fringe of ^2x10 <^-6> and favorable homogeneity.

FIG. 3 is a light transmittance showing a light transmittance curve (I) of a synthetic quartz glass molded body to which a DC voltage is applied and a light transmittance curve (II) of a synthetic quartz glass molded body to which a DC voltage is not applied in Comparative Example 1. It is a curve figure.

FIG. 4 is a light transmittance showing a light transmittance curve (I) of a synthetic quartz glass molded body to which a DC voltage is applied and a light transmittance curve (II) of a synthetic quartz glass molded body to which a DC voltage is not applied in Comparative Example 2. It is a curve figure.

Claims (3)

[Claims] 1. A synthetic quartz glass molded body having no striae in at least the light transmission direction is maintained at a temperature within a range of 800 ° C. to 1500 ° C., and at least 100 DCV is applied to two opposite surfaces of the glass molded body. A method of manufacturing a quartz glass molded body for an excimer laser, which comprises applying a DC voltage of / cm. 2. A synthetic quartz glass molded body having no striae in at least the light transmission direction is maintained at a temperature in the range of 800 ° C. to 1500 ° C., and at least 100 DCV / A method for producing a quartz glass molded body for an excimer laser, which comprises gradually cooling the glass molded body at a cooling rate of 5 ° C./hour or less while applying a DC voltage of cm. 3. A synthetic quartz glass molded body having no striae in at least the light transmission direction is kept at a temperature in the range of 800 ° C. to 1500 ° C., and at least 100 DCV / A method for producing a quartz glass molded body for an excimer laser, which comprises gradually applying a DC voltage of 10 cm and then gradually cooling the glass member at a cooling rate of 5 ° C./hour or less.